What is the role of white blood cells?

• A. they fight off infections
• B. they regulate blood pressure
• C. they carry oxygen
• D. they clot the blood

Answer: (A)

White blood cells are part of the immune system and their main job is to defend the body against infection. They recognize invading pathogens such as bacteria, viruses, and fungi and respond in several ways: some engulf and destroy invaders directly, others produce antibodies or signaling molecules that coordinate and amplify the immune response, and some help recruit more immune cells to the site of infection. This role is distinct from carrying oxygen, which is done by red blood cells, or helping blood to clot, which is the job of platelets and plasma proteins. Blood pressure regulation involves the cardiovascular system and hormones, not white blood cells.